U.S. Pat. No. 5,039,228 issued Aug. 13, 1991 in the name of Richard M. Chalmers for "Fixtureless Environmental Stress Screening Apparatus" ("Chalmers") discloses apparatus having a single vessel adapted to be alternately filled with liquid from separate hot and cold reservoirs so as to alternately apply such liquid in hot form and in cold form to a device in such chamber to the ends of environmentally stressing such device and detecting how it responds to such stress. The liquid disclosed as utilized to produce such thermal cycling stressing is an aliphatic organic compound (e.g., octane) in which all hydrogen atoms have been replaced by flourine, such compound being a liquid sold under the trademark FLOURINERT, a registered trademark of 3M, and available from the 3M Industrial Chemical Products Division, 3M Center Building 223-6S-04, Saint Paul, Minn. 55144-1000. The Chalmers apparatus is of inefficient design for reason among others that it provides only one chamber for thermocyclic stressing of devices, the result being that the times needed between tests of devices to replace one device by another are down times for the apparatus.